1. Field of the Invention
The present invention relates generally to an apparatus for transmitting data between two parts by inductive transmission, including th possibility of simultaneous bidirectional data transmission.
2. Description of the Related Art
In the field of miniaturized circuit devices, such as for use as high security keys and checking (chip) cards particularly in secured entry control, a problem arises of transmitting signals from a circuit of a first part to a circuit of a second part and vice versa. It is desirable that the first part also supplies energy to the second part during the signal transmission and that only one coil be provided at the first part and only one coil be provided at the second part for use in bidirectional signal transmission, as well as for energy transmission.
Monodirectional signal transmission is provided in known systems by using circuits based on the principle of synchronous switching. Signals in the known devices are transmitted from a mobile part, such as a key or chip card, by short circuiting of a coil at defined points in time which are identified by counting oscillation half-waves. Such synchronous switching systems are already in use in the lock and key field.
Inductive oscillation transmission is disclosed in U.S. Pat. No. 4,549,176, and corresponding German Patent Application No. P 31 49 789, although without phase shifts.